Ammoximation process

ABSTRACT

A redox ammoximation process in which a ketone or aldehyde is reacted with ammonia and oxygen in the presence of a catalyst; wherein the catalyst is an aluminophosphate based redox catalyst having at least two different redox catalytic sites comprising different transition metal atoms.

The present invention relates to an ammoximation process using a redoxcatalyst comprising an aluminophosphate, commonly referred to as an“AlPO” system.

AlPO compounds are well known and are known for use as molecular sievesand as catalysts for various processes, for example as described in U.S.Pat. No. 4,567,029, EP0132708, U.S. Pat. Nos. 5,000,931, 4,801,364,5,107,052, 4,853,197, EP0293920, U.S. Pat. Nos. 6,293,999, and6,296,688. They are nanoporous solids with channels permeating the wholeof the material, thus giving the material a very substantial surfacearea, which can be used for catalysis. The basic structure comprisesaluminium and oxygen atoms, in which some of the aluminium atoms havebeen replaced by one or more other atoms, to provide the requiredcatalytic activity.

J. M. Thomas & R. Raja, [Design of a “green” one-step catalyticproduction of ε-caprolactam (precursor of nylon-6), Proceedings Natl.Acad. Sci. USA, 102, 13732-13736 (2005)]; R. Raja, G. Sankar & J. M.Thomas, [Bifunctional molecular sieve catalysts for the benignammoximation of cyclohexanone: One-step, solvent-free production ofoxime and ε-caprolactam with a mixture of air and ammonia, J. Am. Chem.Soc. 123, 8153-8154 (2001)]; and Nature (October 2005, Vol. 437; page1243) describe a process for preparing certain precursors to nylon,especially ε-caprolactam, using such AlPO catalysts, specifically AlPOcatalysts having at least two active sites, one being a redox site,generally based upon Co(III), Mn(III) or Fe(III) atoms, and the otherbeing a Brønsted acid site, generally based on Zn(II), Mg(II) or Co(II)atoms. The two types of site are well separated in the three dimensionalAlPO structure and operate separately on the feedstock. As a result, itis possible to convert the cyclohexanone feedstock into ε-caprolactamwith an efficiency in excess of 70%, up to around 80%, in a single step,rather than use the multi-step procedure currently used—see Nature (opcit).

However, for commercial purposes, a 70% conversion is inadequate, andso, although the reaction proposed in the above literature is veryelegant and of considerable scientific interest, it is presently oflittle commercial value.

Furthermore, there is a desire to produce compounds which can act asintermediates for other useful products. These intermediates includeoximes, especially cyclohexanone-oximes.

We have now surprisingly found that a modification of the catalyst usedin the reaction described above is capable of carrying out ammoximationwith a better yield of up to 100% efficiency. The resulting oxime maythen be converted efficiently, using well known reactions, to thedesired ε-caprolactam. Surprisingly, the two-step reaction issubstantially more efficient than the one-step reaction described in theabove papers.

The present invention provides a redox ammoximation process in which aketone or aldehyde is reacted with ammonia and oxygen in the presence ofa catalyst; wherein the catalyst is an aluminophosphate based redoxcatalyst having at least two different redox catalytic sites comprisingdifferent transition metal atoms. The catalyst may, for example, berepresented by the following qualitative general formula (I) or (II):M¹M²AlPO  (I)or(II):M¹M²SAlPO  (II)in which: M¹ and M² are different from each other and each represents ametal atom having redox catalytic capability, and some of the phosphorus[P(V)] atoms may be replaced by other equivalent atoms. It should benoted that these formulae are purely an indication of the nature of theatoms present and do not represent their relative proportions.

Examples of metals which may be represented by M¹ and M² includeCo(III), Mn(III), Fe(III), Ti(IV), Cr(VI), Cu(III), V(V) and Ru(III).

Some preferred catalyst combinations include (but are not limited to):

-   -   (a) M¹M²AlPO-5 where M¹≡Mn(III) and M²≡Co(III) or Fe(III) or        Ru(III);    -   (b) M¹M²SAPO-5, where M¹≡Co(III), M²≡Mn(III) and additionally        P^(V) can be replaced with Ti(IV), Cr(VI) or V(V);    -   (c) M¹M²AlPO-36 where M¹≡Co(III) and M²≡Mn(III) or Fe(III) or        Ru(III);    -   (d) M¹M²SAPO-36, where M¹≡Mn(III), M²≡Fe(III) and additionally        P^(V) can be replaced with Ti(IV), Cr(VI) or V(V);    -   (e) M¹M²AlPO-31 where M¹≡Fe(III) and M²≡Co(III) or Mn(III) or        Ru(III);    -   (f) M¹ M²SAPO-31, where M¹≡Co(III), M²≡Fe(III) and additionally        P^(V) can be replaced with Ti(IV), Cr(VI) or V(V);    -   (g) M¹ M²SAPO-18, where M¹≡Co(III), M²≡Mn(III) and additionally.        P^(V) can be replaced with Ti(IV), Cr(VI) or V(V);    -   (h) M¹M²AlPO-18 where M¹≡Mn(III) and M²≡Co(III) or Fe(III) or        Ru(III);    -   (i) M¹ M²SAPO-37, where M¹≡Mn(III), M²≡Co(III) and additionally        P^(V) can be replaced with Ti(IV), Cr(VI) or V(V);    -   (j) M¹M²AlPO-37 where M¹≡Fe(III) and M²≡Co(III) or Fe(III) or        Ru(III).

Catalysts of this type are known and processes for their preparation areequally known. Catalysts containing a single redox catalyst site aredescribed, for example, in U.S. Pat. No. 4,567,029, “Catalyticallyactive centres in porous oxides: design and performance of highlyselective new catalysts”, J. M. Thomas and R. Raja, Chem. Comm., 2001,675-687 and “Design of a green one-step catalytic production ofε-caprolactam (precursor of nylon-6)”, J. M Thomas and R. Raja, PNAS,Vol 102/39), 13732-13736. The catalysts with two redox sites can beprepared in a similar manner. Catalysts with two or more redox sites aredescribed in U.S. Pat. Nos. 4,956,165, 4,917,876, 4,801,364 and4,567,029.

In outline the procedure is as follows: the phosphorous source(typically 85% H₃PO₄) and the requisite amount of distilled deionisedH₂O are first mixed, for example gently stirred (400 rpm), for exampleusing a mechanical stirrer in a Teflon-lined autoclave. To this thealuminium source (typically Al(OH)₃) is added, preferably slowly. Thetwo redox metal sources (M¹ and M²) are dissolved in water and thenadded, preferably slowly, to the previously prepared Al—H₃PO₄ mixture(preferably under stirring). An appropriate (depending on the desiredstructure-type) template (structure-directing agent) is then introduced,drop wise, under vigorous stirring (e.g. at 1700 rpm) and the gel isaged, for example, for about 1-2 hours at 298 K. The gel is then heatedin order to synthesize a desired structure-type, for example it may besealed in the Teflon-lined stainless steel autoclave and heated to thedesired temperature, under autogenous pressure, for the required amountof time. The solid product is isolated, preferably by filtration orcentrifugation (after crystallization), washed with copious amounts ofdistilled deionised water and dried under vacuum (90-120° C.). Theas-prepared product is calcined for example at 550° C., first innitrogen for 4 hours and then in dry oxygen for 16 hours, before its useas a catalyst.

Phase purity, structural integrity and crystallinity of the finalcatalyst may be confirmed by using a combination of powder x-raydiffractometry (XRD), X-ray absorption spectroscopy (XAS) and highresolution electron tomography. The precise stoichiometry (with an errorof ca±3×10⁻³) may be determined by ICP (metal) analysis.

The catalysts may be, for example, AlPO-5, 18, 31, 36 or 37 type,preferably of the M¹M²AlPO-5, M¹M²AlPO-18 or M¹M²AlPO-36 type, but arepreferably of the M¹M²AlPO-5 type. Specific preferred examples of thesecatalysts for use in the ammoximation of cyclohexanone areCo^(III)Mn^(III)AlPO-5, Co^(III)Fe^(III)AlPO-5, andMn^(III)Fe^(III)AlPO-5.

In the process of the present invention a ketone or aldehyde is reactedwith ammonia and oxygen. The ketone or aldehyde may be any ketone oraldehyde, for example a C₃-C₂₀ ketone or C₂-C₂₀ aldehyde, and may belinear, branched or cyclic. Preferred ketones are cyclic ketones, forexample C₅-C₁₂ cyclic ketones, with C₆ and C₁₂ ketones being the mostpreferred. Preferred aldehydes contain a cyclic or aromatic ring,especially a C₆ ring. A preferred aldehyde is benzaldehyde. The ketoneor aldehyde may be unsubstituted or substituted, for example by a C₁-C₄alkyl or alkenyl group, —OH or halogen. The ammonia may be in the formof a gas or dissolved in a solvent such as water. Preferably it is inthe form of aqueous ammonium hydroxide. Other than the water presentfrom the aqueous ammonium hydroxide, no additional solvent is normallyneeded but it may be used if desired. The oxygen is provided in the formof a gas, for example as O₂ or air.

The reaction product is generally an oxime corresponding to the ketoneor aldehyde starting material. Thus, for example, the present inventioncan be used for the ammoximation of cyclohexanone tocyclohexanone-oxime, which is a precursor to ε-caprolactam,ε-caprolactam itself being an important precursor to nylon-6, for whichthere is a large and growing market, and so this reaction isparticularly preferred. It can also be used for the ammoximation ofbenzaldehyde to benzaldehyde-oxime. In this reaction, cyclohexanone orbenzaldehyde is reacted with ammonia (generally and preferably in theform of aqueous ammonium hydroxide) and oxygen (which may be provided inthe form of pure oxygen or air) in the presence of the catalyst.

The reaction will take place over a wide range of temperatures andpressures, and the exact temperature and pressure chosen is not criticalto the present invention. However, we generally prefer to carry out thereaction with heating, e.g. a temperature in the range from 50 to 95°C., more preferably from 70 to 90° C. A pressure of, for example, from 1to 500 atmospheres is preferably used, more preferably 1 to 100atmospheres and most preferably 1 to 10 atmospheres. The oxime producedmay be converted into other compounds, for example a lactam. A suitablemethod is described in PNAS 102 (39) 13732-13736 using the Beckmannrearrangement using oleum followed by an acid such as sulphuric acid.

The process of the present invention provides the oxime product in anunexpectedly high conversion rate and at good selectivity. The data inTable 1 of J. Am. Chem. Soc. 2001, 123,8153-4 shows a conversion rate at6 hours of up to 20%. The process of the present invention achieves aconversion rate of at least 50%, preferably at least 70%, as describedin the following Examples.

EXAMPLES General Experimental Setup and Analytical Protocols

The catalytic reactions were carried out in a stainless-steel catalyticreactor (100 ml, Parr) lined with Poly Ether Ether Ketone (PEEK). Thesubstrate (cyclohexanone), ammonia (28% ammonium hydroxide indouble-distilled deionised water) a suitable internal standard(adamantane) and the catalyst (e.g. Co^(III)Mn^(III)AlPO-5, which wasinserted into the sphere of reaction using a specially-designed catalystdelivery system) were then introduced into the reactor, which wassubsequently sealed. The reactor and the inlet and outlet ports werepurged thrice with dry nitrogen prior to reaction. The reactor was thenpressurised with the oxidant (dry air or pure oxygen under dynamicpressure) and the contents were heated to the desired temperature underconstant stirring.

At the end of the reaction, the heating was turned off and the contentsof the reactor were cooled (quenched). The reactor was depressurised anda mass-balance calculation was performed at this stage to check forhandling and mass losses. Where kinetic and rate effects were studied, amini-robot liquid sampling valve was employed to remove small aliquots(0.1 μl) of the sample (aqueous and organic phases) during the course ofthe reaction. The products were analyzed either online (using arobotically-controlled unit with an online computer-controlled systemwhich is linked to a GC and/or LCMS) or offline (using a suitableinternal standard) by gas chromatography (GC, Varian, Model 3400 CX)employing a HP-1 capillary column (25 m×0.32 mm) and flame ionisationdetector using a variable ramp temperature program (from 50° C. to 300°C.). In the offline analysis method, the products were separated and theorganic layer was dried using magnesium sulphate prior to GC analysis.The identities of the products were first confirmed using authenticatedstandards and their individual response factors were determined using asuitable internal standard (adamantane) by the calibration method. Theoverall yields were normalized with respect to the (GC) response factorsobtained as above.

The conversions and selectivities were determined as defined by thefollowing equations and the yields were normalised with respect to theresponse factors obtained as above:Conv. %=[(moles of initial substrate−moles of residual substrate)/(molesof initial substrate)]×100Sel. %=[(moles of individual product)/(moles of total products)]×100

For the internal standard GC method, the response factor (RF) and mol %of individual products were calculated using the following equations:RF=(mol Product/mol Standard)×(Area Standard/Area Product)Mol % Product=RF×Mol Standard×(Area Product/Area Standard)×100/MolSample

The identity of the products was further confirmed using LCMS (ShimadzuLCMS-QP8000), which was again employed either online or offline. Hotfiltration experiments and ICP measurements of the aqueous and organicmixtures were independently carried out to check for the occurrence ofleaching.

Example 1 Ammoximation of Cyclohexanone Using Co^(III)Mn^(III)AlPO-5

This experiment was performed using the protocol described above using25 g of cyclohexanone, 14.6 g of ammonia, 0.5 g of adamantane (theinternal standard), 0.75 of Co^(III)Mn^(III)AlPO-5 (0.10), 30 bar of dryair at 353 K for 6 hours.

The conversion of cyclohexanone to oxidised products was calculated tobe 77% and the selectivity for cyclohexanone oxime was 88%.

Example 2 Ammoximation of Cyclohexanone Using Co^(III)Mn^(III)AlPO-5

This experiment was performed using the protocol described above using25 g of cyclohexanone, 14.6 g of ammonia, 0.5 g of adamantane (theinternal standard), 0.75 of Co^(III)Mn^(III)AlPO-5 (0.10), 15 bar ofpure oxygen at 353 K for 6 hours.

The conversion of cyclohexanone to oxidised products was calculated tobe 71% and the selectivity for cyclohexanone oxime was 84%.

Example 3 Ammoximation of Cyclohexanone Using Co^(III)Fe^(III)AlPO-5

This experiment was performed using the protocol described above using25 g of cyclohexanone, 14.6 g of ammonia, 0.5 g of adamantane (theinternal standard), 0.5 of Co^(III)Fe^(III)AlPO-5 (0.10), 30 bar of dryair at 353 K for 6 hours.

The conversion of cyclohexanone to oxidised products was calculated tobe 56% and the selectivity for cyclohexanone oxime was 89%.

Example 4 Ammoximation of Cyclohexanone Using Mn^(III)Fe^(III)AlPO-5

This experiment was performed using the protocol described above using25 g of cyclohexanone, 14.6 g of ammonia, 0.5 g of adamantane (theinternal standard), 0.5 of Mn^(III)Fe^(III)AlPO-5 (0.10), 30 bar of dryair at 353 K for 6 hours.

The conversion of cyclohexanone to oxidised products was calculated tobe 78% and the selectivity for cyclohexanone oxime was 92%.

Example 5 Ammoximation of Cyclohexanone Using Co^(III)Mn^(III)AlPO-5

This experiment was performed using the protocol described above using15 g of cyclohexanone, 14.6 g of ammonia, 0.5 g of adamantane (theinternal standard), 0.75 of Co^(III)Mn^(III)AlPO-5 (0.10), 30 bar of dryair at 373 K for 6 hours.

The conversion of cyclohexanone to oxidised products was calculated tobe 91% and the selectivity for cyclohexanone oxime was 86%.

Example 6 Ammoximation of Cyclohexanone Using Co^(III)Mn^(III)AlPO-5

This experiment was performed using the protocol described above using15 g of cyclohexanone, 29.2 g of ammonia, 0.5 g of adamantane (theinternal standard), 1.0 of Co^(III)Mn^(III)AlPO-5 (0.10), 30 bar of dryair at 353 K for 6 hours.

The conversion of cyclohexanone to oxidised products was calculated tobe 95% and the selectivity for cyclohexanone oxime was 84%.

Example 7 Ammoximation of Cyclohexanone Using Co^(III)Mn^(III)AlPO-5

This experiment was performed using the protocol described above using14.6 g of ammonia, 0.5 g of adamantane (the internal standard), 0.75 ofCo^(III)Mn^(III)AlPO-5 (0.10), 30 bar of dry air at 353 K for 6 hours.

At the end of the reaction, the heating was turned off and the contentsof the reactor were cooled (quenched). The reactor was depressurised anda mass-balance calculation was performed at this stage to check forhandling and mass losses. 15 g of cyclohexanone, dissolved in 20 g oftoluene was then added to the above reaction mixture and the contentswere stirred for a further 60 minutes at 298 K under nitrogen (5 bar) inthe same reactor. The reactor was then cooled to room temperature beforedepressurising. A mass-balance analysis was carried out at the stage tocheck for handling and other losses. The organic components were thenseparated and dried using magnesium sulphate. The analysis was thenperformed as described earlier in the protocol above.

The conversion of cyclohexanone to oxidised products was calculated tobe 86% and the selectivity for cyclohexanone oxime was 100%.

Example 8 Ammoximation of Cyclohexanone Using Co^(III)Mn^(III)AlPO-5

This experiment was performed using the protocol described above using29.2 g of ammonia, 0.5 g of adamantane (the internal standard), 0.75 ofCo^(III)Mn^(III)AlPO-5 (0.10), 30 bar of dry air at 353 K for 6 hours.

At the end of the reaction, the heating was turned off and the contentsof the reactor were cooled (quenched). The reactor was depressurised anda mass-balance calculation was performed at this stage to check forhandling and mass losses. 15 g of cyclohexanone, dissolved in 20 g oftoluene was then added to the above reaction mixture and the contentswere stirred for a further 60 minutes at 298 K under nitrogen (5 bar) inthe same reactor. The reactor was then cooled to room temperature beforedepressurising. A mass-balance analysis was carried out at the stage tocheck for handling and other losses. The organic components were thenseparated and dried using magnesium sulphate. The analysis was thenperformed as described earlier in the protocol above.

The conversion of cyclohexanone to oxidised products was calculated tobe 88% and the selectivity for cyclohexanone oxime was 100%.

Example 9 Ammoximation of Cyclohexanone Using Co^(III)Fe^(III)AlPO-5

This experiment was performed using the protocol described above using14.6 g of ammonia, 0.5 g of adamantane (the internal standard), 0.75 ofCo^(III)Fe^(III)AlPO-5 (0.10), 30 bar of dry air at 353 K for 6 hours.

At the end of the reaction, the heating was turned off and the contentsof the reactor were cooled (quenched). The reactor was depressurised anda mass-balance calculation was performed at this stage to check forhandling and mass losses. 15 g of cyclohexanone, dissolved in 20 g oftoluene was then added to the above reaction mixture and the contentswere stirred for a further 60 minutes at 298 K under nitrogen (5 bar) inthe same reactor. The reactor was then cooled to room temperature beforedepressurising. A mass-balance analysis was carried out at the stage tocheck for handling and other losses. The organic components were thenseparated and dried using magnesium sulphate. The analysis was thenperformed as described earlier in the protocol above.

The conversion of cyclohexanone to oxidised products was calculated tobe 81% and the selectivity for cyclohexanone oxime was 100%.

Example 10 Ammoximation of Cyclohexanone Using Mn^(III)Fe^(III)AlPO-5

This experiment was performed using the protocol described above using14.6 g of ammonia, 0.5 g of adamantane (the internal standard), 0.75 ofMn^(III)Fe^(III)AlPO-5 (0.10), 30 bar of dry air at 353 K for 6 hours.

At the end of the reaction, the heating was turned off and the contentsof the reactor were cooled (quenched). The reactor was depressurised anda mass-balance calculation was performed at this stage to check forhandling and mass losses. 15 g of cyclohexanone, dissolved in 20 g oftoluene was then added to the above reaction mixture and the contentswere stirred for a further 60 minutes at 298 K under nitrogen (5 bar) inthe same reactor. The reactor was then cooled to room temperature beforedepressurising. A mass-balance analysis was carried out at the stage tocheck for handling and other losses. The organic components were thenseparated and dried using magnesium sulphate. The analysis was thenperformed as described earlier in the protocol above.

The conversion of cyclohexanone to oxidised products was calculated tobe 94% and the selectivity for cyclohexanone oxime was 100%.

Example 11 Ammoximation of Cyclohexanone Using Co^(III)Mn^(III)AlPO-5

This experiment was performed using the protocol described above using29.2 g of ammonia, 0.5 g of adamantane (the internal standard), 0.75 ofCo^(III)Mn^(III)AlPO-5 (0.10), 30 bar of dry air at 373 K for 8 hours.

At the end of the reaction, the heating was turned off and the contentsof the reactor were cooled (quenched). The reactor was depressurised anda mass-balance calculation was performed at this stage to check forhandling and mass losses. 15 g of cyclohexanone, dissolved in 20 g oftoluene was then added to the above reaction mixture and the contentswere stirred for a further 60 minutes at 298 K under nitrogen (5 bar) inthe same reactor. The reactor was then cooled to room temperature beforedepressurising. A mass-balance analysis was carried out at the stage tocheck for handling and other losses. The organic components were thenseparated and dried using magnesium sulphate. The analysis was thenperformed as described earlier in the protocol above.

The conversion of cyclohexanone to oxidised products was calculated tobe 97% and the selectivity for cyclohexanone oxime was 94%.

The invention claimed is:
 1. A redox ammoximation process comprisingreacting a ketone with ammonia and oxygen in the presence of a catalystto form a cyclohexanone-oxime; wherein the catalyst is analuminophosphate based redox catalyst having the formula (I):M¹M²AlPO-5  (I) wherein M¹ and M² each represents a different atomselected from Co(III), Mn(III) and Fe(III).
 2. A process according toclaim 1 wherein the catalyst isCo^(III)Mn^(III)AlPO-5,Co^(III)Fe^(III)AlPO-5 or Mn^(III)Fe^(III)AlPO-5.3. A process according to claim 1 wherein the ammonia is in the form ofaqueous ammonium hydroxide.
 4. A process according to claim 1 furthercomprising carrying out the process at a temperature in the range from50 to 95° C.
 5. A process according to claim 4 further comprisingcarrying out the process at a temperature in the range from 70 to 90° C.